Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
U.S. Pat. No. 4,451,561 discloses a heat-development-type image recording material comprising on a support a heat-development-type image recording layer containing (a) an organic silver salt, (b) a reducing agent, (c) a binder, and (d) at least one compound of following formula [I]:
wherein R1 represents a hydrogen atom, a hydroxy radical or a substituted or unsubstituted alkyl, alkenyl, aryl or alkoxy radical; Y represents a sulfonyl or a carbonyl radical; and X represents a sulfur atom or ═N—R2 wherein R2 is a hydrogen atom, an amino radical or a substituted or unsubstituted alkyl, aryl or alkenyl radical. U.S. Pat. No. 4,451,561 further discloses the presence of an additional compound of following formula [II]:
wherein R3 represents a substituted or unsubstituted alkyl, aryl or heterocyclic radical; R4 and R5 each represent a hydroxy or a substituted or unsubstituted alkyl, aryl or heterocyclic radical; Z represents a hydroxy or an amino radical; and m is an integer of 1 or 2. Specifically the following compounds according to formula [I] are disclosed:
and the following compounds according to formula (II) are disclosed:

U.S. Pat. No. 4,543,309 discloses a heat-developable image-pattern recording material of enhanced developability and stability having on a support a heat-developable image-pattern recording layer containing (a) a silver salt of a benzotriazole, (b) a reducing agent, (c) a binder, (d) at least one compound having the following formula:
wherein R1 represents a hydrogen, an amino radical, or a substituted or unsubstituted alkyl, alkenyl or aryl radical; R2 represents a hydrogen, an amino, alkyl, alkenyl or aryl radical; and further contains a compound of the formula:
wherein R3 represents a substituted or unsubstituted alkyl, aryl or heterocyclic radical; R4 and R5 each represent a hydroxy or a substituted or unsubstituted alkyl, aryl or heterocyclic radical; Z represents a hydroxy or an amino radical; and m is an integer of 1 or 2. Specifically the following compounds according to formula (II) are disclosed:

U.S. Pat. No. 5,374,514 discloses a photothermographic material comprising photographic silver halide, a reducible silver source, a reducing agent for silver ion, and a binder, and, as an antifoggant and/or image stabilizer, a compound of the formula:
wherein: R is a member selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group and a heterocyclic group.
JP 09-295456 discloses a method of obtaining an image which is long in shelf life and high in density, wherein at least one side of an organic silver salt or developer of organic silver salt is contained in a heat response property micro-capsule, and at least one kind in a group of compounds of a specific formula as a fog inhibitor is contained in a recording layer, the group of compounds including 1-thia-3,4-diazole-tribromomethylsulfone.
EP-A 0 713 133 discloses a thermal imaging system consisting of (i) a donor element comprising on a support a donor layer containing a binder and a thermotransferable reducing agent capable of reducing a silver source to metallic silver and (ii) a receiving element comprising on a support a receiving layer comprising a silver source, capable of being reduced by means of heat in the presence of a reducing agent, a binder and a stabiliser selected from the group consisting of benzotriazoles, heterocyclic mercaptanes, sulphinic acids, 1,3,4-triazo-indinolines, 1,3-dinitroaryl compounds, 1,2,3-triazoles, phthalic acids and phthalic acid derivatives.
EP-A 0 901 040, which corresponds to U.S. Pat. No. 6,348,308, discloses a substantially light-insensitive monosheet recording material comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, characterized in that said thermosensitive element further contains an unsaturated carbocyclic or heterocyclic stabilizer compound substituted with a —SA group where A is hydrogen, a counterion to compensate the negative charge of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide and said recording material is capable of producing prints with a numerical gradation value defined as the quotient of the fraction (2.5−0.1)/(E2.5−E0.1) greater than 2.3, where E2.5 is the energy in Joule applied in a dot area of 87 μm×87 μm of the imaging layer that produces an optical density value of 2.5, and E0.1 is the energy in Joule applied in a dot area of the imaging layer material that produces an optical density value of 0.1.
WO 94/16361 discloses a multilayer heat-sensitive material which comprises: a color-forming layer comprising: a color-forming amount of finely divided, solid colorless noble metal or iron salt of an organic acid distributed in a carrier composition; a color-developing amount of a cyclic or aromatic organic reducing agent, which at thermal copy and printing temperatures is capable of a color-forming reaction with the noble metal or iron salt; and an image-toning agent; characterized in that (a) the carrier composition comprises a substantially water-soluble polymeric carrier and a dispersing agent for the noble metal or iron salt and (b) the material comprises a protective overcoating layer for the color-forming layer. Furthermore, WO 94/16361 discloses that suitable antifoggants are well-known photographic anti-foggants such as mercaptobenzotriazole, chromate, oxalate, citrate, carbonate, benzotriazole (BZT), 5-methylbenzotriazole, 5,6-dimethylbenzotriazole, 5-bromobenzotriazole, 5-chlorobenzotriazole, 5-nitro-benzotriazole, 4-nitro-6-chlorobenzotriazole, 5-nitro-6-chlorobenzotriazole, 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, benzimidazole, 2-methylbenz-imidazole, 5-nitrobenzimidazole, 1-phenyl-5-mercaptotetrazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptothiazoline, 2-mercapto-4-methyl-6,6′-dimethylpyrimidine, 1-ethyl-2-mercapto-5-amino-1,3,4-triazole, 1-ethyl-5-mercapto-1,2,3,4-tetrazole, 2,5-dimercapto-1,3,4-thiodiazole, 2-mercapto-5-aminothiodiazole, dimethyldithiocarbamate, and diethyldithiocarbamate.
U.S. Pat. No. 5,558,983 discloses a photothermographic element comprising a support bearing at least one photosensitive, image-forming, photothermographic emulsion layer comprising: (a) a photosensitive silver halide; (b) a non-photosensitive, reducible silver source; (c) a reducing agent system for silver ion; and (d) a binder; wherein said reducing agent system comprises: (i) at least one hindered phenol; (ii) at least one co-developer of the formula R1—(C═O)—NHNH—R2 wherein: R1 represents hydrogen and R2 represents an aryl or substituted aryl group; or, R1 represents hydrogen, alkyl, or alkenyl groups of 1 to 20 carbon atoms; alkoxy, thioalkoxy, or amido groups of 1 to 20 carbon atoms; aryl, alkaryl, or aralkyl groups of up to 20 carbon atoms; aryloxy, thioaryloxy, or anilino groups of up to 20 carbon atoms; aliphatic or aromatic heterocyclic ring groups containing up to 6 ring atoms; carbocyclic ring groups comprising up to 6 ring carbon atoms; or fused ring or bridging groups comprising up to 14 ring atoms; and R2 represents a trityl group; and (iii) at least one N-acyl-hydrazine compound of the formula R3—(C═O)—NH—NH2 wherein: R3 represents an alkyl or alkenyl groups of 1 to 20 carbon atoms; alkoxy, thioalkoxy, or amido groups of up to 20 carbons; aryl, alkaryl or aralkyl groups comprising up to 20 carbon atoms; aryloxy, thioaryloxy, or anilino groups of up to 20 carbon atoms; aliphatic or aromatic heterocyclic ring groups containing up to 6 ring atoms; carbocyclic ring groups comprising up to 6 ring carbon atoms; or fused ring or bridging groups comprising up to 14 ring atoms. U.S. Pat. No. 5,558,983 also discloses a thermographic element comprising a support bearing at least one, image-forming, thermographic emulsion layer comprising: (a) a non-photosensitive, reducible silver source; (b) a reducing agent system for silver ion; and (c) a binder; wherein said reducing agent system comprises: (i) at least one hindered phenol; (ii) at least one co-developer of the formula R1—(C═O)—NHNH—R2 wherein: R1 represents hydrogen and R2 represents an aryl group; or, R1 represents hydrogen, alkyl or alkenyl groups of 1 to 20 carbon atoms; alkoxy, thioalkoxy, or amido groups of 1 to 20 carbon atoms; aryl, alkaryl, or aralkyl groups of up to 20 carbon atoms; aryloxy, thioaryloxy, or anilino groups of up to 20 carbon atoms; aliphatic or aromatic heterocyclic ring groups containing up to 6 ring atoms; carbocyclic ring groups comprising up to 6 ring carbon atoms; or fused ring or bridging groups comprising up to 14 ring atoms; and R2 represents a trityl group; and (iii) at least one N-acyl-hydrazine compound of the formula R3—(C═O)—NH—NH2 wherein R3 represents an alkyl or alkenyl groups of 1 to 20 carbon atoms; alkoxy, thioalkoxy, or amido groups of 1 to 20 carbons; aryl, alkaryl or aralkyl groups comprising up to 20 carbon atoms; aryloxy, thioaryloxy, or anilino groups of up to 20 carbon atoms; aliphatic or aromatic heterocyclic ring groups containing up to 6 ring atoms; carbocyclic ring groups comprising up to 6 ring carbon atoms; or fused ring or bridging groups comprising up to 14 ring atoms. Furthermore, U.S. Pat. No. 5,558,983 also discloses the compound CA-3:

GB-A 1,501,005 discloses a sensitive photothermographic material which comprises a support coated on one side with a composition containing (a) a photographic silver halide, (b) an image-forming combination comprising (i) a silver salt of a heterocyclic thione of the formula
wherein R represents atoms which complete an unsubstituted or substituted heterocyclic ring and Z is an alkylene group having from 1 to 30 carbon atoms and (ii) an organic reducing agent therefor, and (c) a toner which is a mercaptoheterocyclic compound which gives by the test procedure specified herein, a δD value of from zero to 0.21, the components of the composition being disposed in one or more layers.